Mandrel for gas lift valves



Dec. 8, 1964 D. c. MEYERS 3,160,113

MANDREL FOR GAS LIFT VALVES Filed Nov. 24, 1961 Q/IO INVENTORZ DOUGLAS C. MEYERS BY; h

HIS AGENT 3,160,113 .MANDREL FUR GAS LIFT VALVES Douglas C. Meyers, ,h fetairie, La, assignor to Shell @il Company, New York, N.Y., a corporation of Delaware Filed Nov. 24, 1%1, Ser. No. 154,566 3 tClaims. (Qt. 1433-232) The present invention relates to improvements in well production apparatus, and, more particularly to an improved gas lift valve mandrel.

Since many oil formations contain considerable amounts of water, the oil recovered therefrom is often accompanied by water. In the production of oil from such formations by means of the gas lift method, it has been found that the conventional apparatus for admitting lifting gas into a production string from a well casing often produces a homogeneous oil-water emulsion in the string which makes subsequent separation of the oil from the water very expensive with'respect to both the installation and operation of treating equipment. Ernulsification of the fluid in the production string occurs when the velocity of gas injected into the string through controlling gas lift valves reaches a critical value. Critical velocity occurs at any time the pressure of the fiuid in the production string is .58 or less times that of the pressure of the gas entering the controlling valve orifice.

If the pressure in the production string is .58 or less times the pressure in the casing, the gas injected into the production string from the controlling valve expands explosively to the pressure in the production string, thereby producing an atomization of the fluid in the production string in much the same manner as the familiar atomizer or spray gun. The atomization of a fluid in the production string containing a mixture of oil and water produces the aforementioned emulsification.

Commercially available gas lift equipment is employed with a well casing having a centrally disposed production string for removal of the oil. In the gas lift process, gas is generally maintained in the well casing at pressures above that necessary to obtain critical velocities when admitted into the string through controlling gas lift valves. The presently known systems make no adequate provisions to prevent gas from entering the string at critical velocities and, as a result, oil-water emulsification and consequent processing expenses are certain to occur.

An object of the present invention is, therefore, to provide an apparatus whereby the gas lift method may be used without emulsification of the lifted medium.

Another object of this invention is to prevent oil-water emulsification while utilizing commercially available gas lift equipment.

Still another object of this invention is to provide a relatively inexpensive and trouble-free means of minimizing oil-water emulsification when using the gas lift process.

In its broadest aspect the invention includes a gas lift valve mandrel provided with an expansion chamber having an injection opening communicating with the medium being lifted and an opening in communication with a gas lift valve proper. The areas of the injection opening and valve orifice are calculated and constructed so as to prevent gas from entering the lifted medium at critical velocities.

More specifically, the invention comprises a mandrel afiixed to a production string; said mandrel having a first opening communicating with the interior of the string and a second opening at the exterior of the string, an expansion chamber connecting said openings, and provision on said second opening to facilitate connection of a gas lift valve.

Referring to the drawing, the single figure thereof represents a sectional elevation view of a device constructed lidfiddl Patented Dec. 8, 1964 in accordance with the invention. Conventional gas lift structures above and below the inventive mandrel are broken away in order to simplify the illustration.

In the drawing, the numeral 1 designates a Well casing having a centrally disposed production string 2 extending therethrough. A gas lift mandrel 3, wherein the invention primarily resides, is disposed within the well casing and afiixed to the string 2. The mandrel includes an expansion chamber 4 having a lower fluid port or opening 5 communicating with the interior of the production string and an upper fluid port or opening 6 provided with threads 7 to receive a gas lift valve. Opening 5 is preferably disposed at the lower end of the expansion chamher in order to assure that liquid is not in the chamber when gas is being injected.

The numeral 10 designates one form of a relatively conventional gas lift valve having a housing 11 secured to the mandrel by threads 12 received in threads '7 of the mandrel. An annular gasket 13 is interposed between the valve housing and the mandrel to insure a sealed connection therebetween. The valve further includes inlet ports 14 and 15 for admitting gas into the valve and an outlet orifice 17 for admitting gas into the expansion chamber of the mandrel. Flow through the valve is controlled by a reciprocating valve element 18 adapted to seat the upper end of the outlet orifice 17. The reciprocating valve element 18 is actuated by pressure-responsive bellows 2e secured to the valve housing through plate 21 and bolts 22.

In operation the disclosed gas lift apparatus is relatively conventional in that it introduces gas into the oil and water mixture present in the string. Gas under pressure is maintained in the space between the tubing string 2 and the well casing 1 and is admitted into the tubing string 2 at predetermined pressures. Admission pressure may be controlled by selecting and/or adjusting a valve it; having desired pressure characteristics.

The apparatus of the present invention constitutes an improvement over conventional gas lift apparatus in that it facilitates the introduction of gas into a production string without emulsification of the oil-water mixture present in the string. Emulsification of oil and water in conventional gas lift apparatus occurs due to the explosive disturbance created in the lifted medium when the lifting gas is injected into the production string at critical velocities. Velocity is critical Whenever the pressure in the production string is .58 or less times that of the gas entering the orifice of the gas lift valve used to inject gas into the string.

In the present invention critical velocity occurs at the exit of the orifice 17. However, due to the presence of only gas in the expansion chamber 4, the explosive ex pansion occurs in this chamber and there is little, if any, further expansion at the opening 5 when the gas is mixed with the lifted medium. It is noted that before the orifice 17 is opened, the pressure of the gas present in chamber 4 is approximately equal to that of the lifted medium in reduction string 2.

The area of the orifice 17 used in the mandrel and valve combination is determined to regulate the rate and volume of the gas injected into the production string in much the same manner that chokes are used to control the rate of production from oil and gas wells. The area of the opening 5 used in combination with a particular orifice 17 is determined to prevent gas from entering the production string 2 at critical velocities. A method of calculating the area ofthe inlet opening 5 will be developed in the following paragraphs.

Since pressure in the well casing 1 is generally very high relative to the pressure in the production string 2 and expansion chamber 4, it may be assumed that critical flow will exist at the orifice 17 of the gas lift valve 10. Critical pressure at an orifice (such as the orifice 17) is approximately .58 times the pressure upstream of the orifice (pressure in the well casing in the present case) and occurs when the velocity ofthe gas passing through the orifice is equal to the speed of sound in the gas. In the present case it has been found desirable to determine the area of the injection port 5 so that the velocity at this point is equal to or less than the velocity at the valve orifice. Therefore, assuming critical flow at the orifice 17 and knowing pressure at the orifice is approximately .58 times pressure in the well casing, a formula for determining the area of the port 5 may be derived as shown below.

'To simplify the derivation the following symbols will be used:

(1) It has been found desirable to determine the area of the injection port 5 so that velocity at this point is equal to or less than the assumed critical velocity at the valve orifice 17.

Vel gVel (2) Velocity is a function of volume per unit time and area.

Volume/Time Velocity Area (3) Therefore 1 with (l) Vol /a inee Vol /Time T Velc (4) Boyles law, if temperature remains constant volume varies inversely with pressure or,

Pressure Volume=Constant Since critical flow is assumed at A P, v01,==P, vo1

: P, Vol

(5) Substituting in (3) (6) Since P a $9458 .58P XA Since P P and A are readily determinable, it can 58 (The pressure of the volume of) 4 be seen that A may be easily calculated by the above derived formula;

From the formula, it can also be seen that or that the areas of the injection port and valve orifice are approximately inversely proportional to those pressures at the respective areas.

To summarize, the present invention provides a means of injecting gas into a production string at sub-critical velocity While maintaining high pressure in the well casing; The invention is accomplished through the use of a valve mandrel having an expansion chamber and an enlarged injection port. Installation cost of the invention is held to a minimum since it facilitates the use of conventional gas lift valves, casings and production strings.

The foregoing description of the invention is merely intended to be explanatory thereof. Various changes in the details of the illustrated construction may be made, within the scope of the appended claims, without departing from the spirit of the invention.

I claim as my invention:

1. A gas lift valve assembly for use in injecting gas into the upper end of the interior of a Well production string from a volume of gas under pressure at the exterior of the production string, said assembly comprising:

a mandrel fixed to the production string and having an expansion chamber formed therein, said mandrel having an injection port extending therethrough directly between the lower end of said chamber and the interior of the production string,

valve housing carried by said mandrel and having an outlet orifice extending directly into the interior of said chamber, said chamber being dimensioned so as to permit substantially complete expansion of the gas therein under well pressure conditions existing, said valve housing having further an inlet port communicating the volume of gas at the exterior of the production string with said outlet orifice;

control means carried by said valve housing to control fluid flow through said outlet orifice and wherein the areas of the injection port and the outlet orifice are so proportioned relative to each other that gas flowing through said port enters the production string at less than critical velocity.

2. An assembly according to claim 1 wherein the injection port extends upwardly from the chamber to the interior of the production string.

3. An assembly according to claim 1 wherein (The area of the injection port) 2 gas under pressure to the ex- The area of terior of the production string outlet orifice (The pressure in the interior of the production string) References Cited in the file of this patent UNITED STATES PATENTS 1,363,198 Oliphant Dec. 21, 1920 2,345,865 Boynton Apr. 4, 1944 2,478,483 Hartman Aug. 9, 1949 2,948,232 McCarvell Aug. 9, 1960 

1. A GAS LIFT VALVE ASSEMBLY FOR USE IN INJECTING GAS INTO THE UPPER END OF THE INTERIOR OF A WELL PRODUCTION STRING FROM A VOLUME OF GAS UNDER PRESSURE AT THE EXTERIOR OF THE PRODUCTION STRING, SAID ASSEMBLY COMPRISING: A MANDREL FIXED TO THE PRODUCTION STRING AND HAVING AN EXPANSION CHAMBER FORMED THEREIN, SAID MANDREL HAVING AN INJECTION PORT EXTENDING THERETHROUGH DIRECTLY BETWEEN THE LOWER END OF SAID CHAMBER AND THE INTERIOR OF THE PRODUCTION STRING, A VALVE HOUSING CARRIED BY SAID MANDREL AND HAVING AN OUTLET ORIFICE EXTENDING DIRECTLY INTO THE INTERIOR OF SAID CHAMBER, SAID CHAMBER BEING DIMENSIONED SO AS TO PERMIT SUBSTANTIALLY COMPLETE EXPANSION OF THE GAS THEREIN UNDER WELL PRESSURE CONDITIONS EXISTING, SAID VALVE HOUSING HAVING FURTHER AN INLET PORT COMMUNICATING THE VOLUME OF GAS AT THE EXTERIOR OF THE PRODUCTION STRING WITH SAID OUTLET ORIFICE; CONTROL MEANS CARRIED BY SAID VALVE HOUSING TO CONTROL FLUID FLOW THROUGH SAID OUTLET ORIFICE AND WHEREIN THE AREAS OF THE INJECTION PORT AND THE OUTLET ORIFICE ARE SO PROPORTIONED RELATIVE TO EACH OTHER THAT GAS FLOWING THROUGH SAID PORT ENTERS THE PRODUCTION STRING AT LESS THAN CRITICAL VELOCITY. 